The invention concerns an interface device for a bi-directional low voltage/radio frequency carrier LC-LV connection between a low voltage electrical energy distribution line, enabling the transmission of signals by carriers, and radio space.
At present, the transmission of messages such as management messages by carriers on a low voltage electrical energy distribution network, LV network, with the view to ensuring the management of different services to which clients subscribed to this electrical energy distribution network have access, is more and more used, on account, on the one hand, of the pre-existence of access to electrical energy distribution installations, and, on the other hand, of the potential growth at least of these types of services likely to be offered.
In a general way, a concentrator device is provided, as shown in an illustrative manner in FIG. 1a, for a branch of the low voltage electrical energy distribution network, running from the HV/LV transformer for example.
This concentrator device connected through a telephone connection for example with a management center, enables management messages to be sent on the LV network according to a credit repetition process. The installations of each subscriber involved with the services are equipped with a Clientele Communicating Interface circuit, I.C.C. circuit, branched between one of the phase conductors and the network neutral. The management messages, transmitted for example by the concentrator, on a call from the management center, in a semi-interactive mode, are propagated, in correct reception conditions on the LV network, over a distance not exceeding about 200 to 300 meters. For this reason, the transmission process of the management messages is composed of a repetition process with credit repetition, every I.C.C. circuit receiving from the upstream, i.e. from the commutator itself or from the upstream I.C.C. circuit, a management message which is not intended for it carrying out a decrementation of one unit of the credit repetition then a retransmission of the received message, with a decremented credit repetition. This process, ensuring a transmission in waves of different management messages, such as shown in an illustrative way in FIG. 1b. allows in this way every I.C.C. circuit to be reached, whatever its position on the LV network. The credit repetition is for example carried to zero when the specified management address message has reached the I.C.C. circuit of corresponding specified address, and the initial credit repetition allocated by the concentrator is chosen as a function of the equipment configuration of the LV network and of specific security criteria allowing the repetition by the concentrator of the management message provided from its credit repetition.
In the aforesaid current technical state of the art, the throughput rate of transmitted data, i.e. the management messages, is 300 bits/second. Such a transmission rate allows temporarily slowing the data frame, carriers of these messages, to the frequency of the LV network, 50 Hz, whatever the phase conductor on which an I.C.C. circuit is branched.
The transmission mode is of the bi-directional half-duplex transmission half-duplex carrier type at 61 kHz and at 74 kHz respectively, each representing respectively the binary value of 0 and 1.
It then follows that for a repetition, all the bits are transmitted in a synchronous way. The 61 and 74 kHz carriers cannot however be synchronized. The initiative of the exchange is due at the present time to the single concentrator. The response of the addressee I.C.C. circuit gets, in the same way as the concentrator-I.C.C. circuit call, the repetition with the same credit repetition value. For the data frames the duration of which is of the order of one second and takes account of an initial credit repetition of the order of 3 or 4, it can be estimated that the duration of a management message exchange between the concentrator and a given I.C.C. circuit is of the order of 10 to 12 seconds.
For a more detailed description of the characteristics of carrier signals, LC-LV signals, the European standard EN 50065-1 can be usefully referred to. By reference to the aforementioned standard, it is simply indicated that the type of modulation used by the low frequency carriers at 61 kHz and 74 kHz is the SFSK modulation, for Spread Frequency Shift Keying, this type of modulation being included as an FSK modulation mode for which the spectral lines are sufficiently distant from each other to avoid the disturbance of one by a noise or interference in practice being able to reach the other. In such a case, the receiver processes the undisturbed line as if it was a simple transmission in O-O-K mode for ON-OFF KEYING.
Thus, a one logic is shown by the presence of the low frequency carrier at 61 kHz and the absence of the low frequency carrier at 74 kHz, and a zero logic by the absence of the low frequency carrier at 61 kHz and the presence of the low frequency carrier at 74 kHz.
The aforementioned operating mode gives satisfaction. However, it has an obvious limitation, insofar as the line equipment of the LV network, in concentrators being mainly reserved to the lines having a sufficient density of subscribed clients is concerned. It is hardly ever conceivable to ensure a generalization and an extension of the provision of services whatever the size of the LV network and the subscribed client density on this LV network.